Kamen G. Usunoff

Part II starts with a systemic model of the basal ganglia to evaluate the position of the STN in the direct, indirect and hyperdirect pathways. A summary of in vitro studies is given, describing STN spontaneous activity as well as responses to depolarizing and hyperpolarizing inputs, and high frequency stimulation. STN bursting activity and the underlying ionic mechanisms are investigated. Deep brain stimulation used for symptomatic treatment of Parkinson’s disease is discussed in terms of the elements that are influenced and its hypothesized mechanisms. This part of the monograph pays attention to the pedunculopontine-subthalamic connections and tries in cell cultures to mimic neurotransmitter actions of the pedunculopontine nucleus and high frequency stimulation on cultured dissociated rat subthalamic neurons. STN cell models: single and multi compartment, and system level models are discussed in relation to subthalamic function and dysfunction. Part I and II are mutually compared.

1 Introduction 1.1 Hemiballism Hemiballism or hemichorea is a rare neurological disorder, but the crucial invol- ment of the subthalamic nucleus (STN) in its pathophysiology has been app- ciated for decades (Jakob 1923; Martin 1927; Glees and Wall 1946; Whittier and Mettler 1949; Carpenter and Carpenter 1951; Crossman 1987). Only recently have serious doubts come forward. Postuma and Lang (2003) have described the STN as being involved in only a minority of cases, and indicated unrecognized causes such as non-ketotic hyperosmolar hyperglycaemia and complications of human immunodeficiency virus (HIV) infections. Moreover, the crucial involvement of a lesion of the STN is in doubt (Guridi and Obeso 2001; Postuma and Lang 2003). On the other hand, idiopathic Parkinson's disease (Battistin et al. 1996; Usunoff et al. 2002) is a common neurodegenerative disorder, but the key role of the STN in the pathophysiological origin of the parkinsonian state has become evident only recently (Miller and DeLong 1987; Mitchell et al. 1989; Bergman et al. 1990, 1994; Hollerman and Grace 1992; Guridi et al. 1993; Parent and Hazrati 1995b; Hassani et al. 1996; Levy et al. 1997, 2002; Blandini et al. 2000; Hirsch et al. 2000; Ni et al.

This monograph offers a comprehensive review of present knowledge of the structure and connections of the trigeminal nuclei in humans, and compares it to laboratory animal findings. The authors provide cytoarchitectural data from their own research, and trace trigeminal pathways in human material by means of the Nauta technique. In humans the trigeminal nuclear complex includes the motor nucleus, the principal sensory (pontine) nucleus, the spinal nucleus (subdivided into oral, interpolar and caudal nuclei), and the mesencephalic nucleus and several small nuclei. The supratrigeminal nucleus, as described in various mammals, is not defined in the human brain. The primary afferents to all subdivisions of the trigeminal nuclear complex in humans appear to be entirely ipsilateral. Some of the 'extratrigeminal' primary afferents described in experimental animals are also present in the human brain and the nucleus ovalis receives primary and possibly secondary afferents from the trigeminal systems. A significant difference between the human trigeminal system and the subprimate species is seen in the monosynaptic cortical projection to the motor trigeminal nucleus.